Method and system for extracting heat from a flue gas

ABSTRACT

A system is provided for extracting heat from a flue gas after it is expelled from a cooking appliance, such as a commercial deep fryer. A flue extension is provided between the flue of the cooking appliance and an exhaust hood positioned above the cooking appliance. Within the flue extension is disposed a heat exchanger assembly, which includes a coil that forms part of a closed fluid loop including a second heat exchanger that is disposed within a fluid medium that is to be heated, such as water. A mount supports the flue extension, and allows movement of the flue extension between an operating configuration and a stowed configuration. The flue extension is positioned closer to the flue of the cooking appliance when in the operating configuration compared to the stowed configuration. Mounting the flue extension is achieved without modifying the cooking appliance or the exhaust hood.

FIELD OF THE INVENTION

The present invention relates generally to the field of waste heat recovery. More particularly, the present invention relates to a method and system for extracting heat from flue gas that is exiting from a cooking appliance, such as for instance a commercial deep fryer or gas oven.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Canadian Patent Application No. 2911796, filed Nov. 12, 2015, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

In the restaurant industry, and in other settings in which commercial cooking appliances are used, it is required to vent waste heat to the outside via an exhaust hood that is positioned above the cooking appliance. Unfortunately, this practice results in a very inefficient use of energy in the kitchen. For instance, the flue gas from a commercial deep fryer may be exhausted at a temperature in the range 700-1100° F. At the same time, additional energy is consumed for space heating and to heat water for other applications in the kitchen, such as dish washing, hand cleaning, etc.

Various attempts have been made to partially recover the waste heat that is produced by commercial cooking appliances, to be used for other purposes such as space heating and/or production of hot water. In one approach a heat exchanger is located within the exhaust hood above the appliance for extracting heat from the air as it is being vented to the outside. This approach is not entirely satisfactory because grease and other particulates tend to build up rather quickly on the heat-exchanger surfaces, thereby insulating the surfaces and reducing the efficiency of the system over time. Further, the temperature of the air that enters the exhaust hood is much lower than the temperature of the air immediately after it exits the flue of the cooking appliance, and as such less heat is available to be extracted. In another approach a heat exchanger is introduced directly into the flue of the cooking appliance. This approach is also not entirely satisfactory because the heat exchanger is subjected to extremely high temperatures, which necessitates a very robust design and may cause solder joints etc. to fail relatively quickly. Additionally, modifying the cooking appliance to accept the heat exchanger within the flue may violate safety code regulations and/or void manufacturer warranties.

SUMMARY OF THE INVENTION

In accordance with an aspect of at least one embodiment, there is provided a system for extracting heat from a flue gas exiting from a cooking appliance, the system comprising: a flue extension having an open first end and an open second end opposite the first end, the first end aligned with but spaced apart from a flue of the cooking appliance for receiving a flue gas at a first temperature as it exits via the flue of the cooking appliance, and the second end facing but spaced apart from an exhaust hood for discharging the flue gas at a second temperature to the exhaust hood, the second temperature being lower than the first temperature; a mount for supporting the flue extension within a space between the flue of the cooking appliance and the exhaust hood, the mount being other than secured to either the cooking appliance or the exhaust hood; and a heat exchanger assembly disposed within the flue extension and comprising a heat exchanger tube for circulating a volume of a thermal fluid, the heat exchanger tube comprising a plurality of substantially straight tube sections that are arranged substantially normal to a flow direction of the flue gas through the flue extension.

In accordance with an aspect of at least one embodiment, there is provided a system for extracting heat from a flue gas exiting from a cooking appliance, comprising: a flue extension having an open first end, an open second end that is opposite the first end, and a central passageway extending between the first and second ends; a first heat exchanger assembly disposed within the central passageway of the flue extension; a mount for supporting the flue extension and the first heat exchanger within a space between a flue of the cooking appliance and an exhaust hood disposed above the cooking appliance, the mount being operable between: a first configuration in which the first end of the flue extension is aligned with but spaced apart from the flue of the cooking appliance by a first distance, and a second configuration in which the first end of the flue extension is spaced apart from the flue of the cooking appliance by a second distance that is greater than the first distance; a storage tank for containing a medium to be heated; a second heat exchanger disposed within the storage tank, the second heat exchanger being in fluid communication with the first heat exchanger; and a pump for circulating a thermal fluid within a closed circuit that includes the first heat exchanger and the second heat exchanger.

In accordance with an aspect of at least one embodiment, there is provided a method for extracting heat from a flue gas exiting a cooking appliance, comprising: using a mount, supporting a flue extension between a flue of the cooking apparatus and an exhaust hood disposed above the cooking apparatus, such that an open first end of the flue extension is aligned with but spaced apart from the flue of the cooking apparatus by a first distance, and wherein the mount is other than secured to either the cooking appliance or the exhaust hood; providing a heat exchanger assembly within the flue extension, the heat exchanger assembly including a heat exchanger coil; receiving the flue gas via the open first end of the heat exchanger, the flue gas being constrained by the flue extension to flow around the heat exchanger coil and out through an open second end of the flue extension along a direction generally toward the exhaust hood; and while the flue gas is being constrained to flow around the heat exchanger coil, circulating a heat transfer fluid within the heat exchanger coil, whereby heat is transferred from the flue gas to the thermal fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The instant invention will now be described by way of example only, and with reference to the attached drawings, wherein similar reference numerals denote similar elements throughout the several views, and in which:

FIG. 1 is a block diagram showing the components of a system according to an embodiment.

FIG. 2 is a schematic diagram showing a system according to an embodiment.

FIG. 3 is a diagram showing the components of a sensing and control sub-system.

FIG. 4 is a perspective view of a flue extension secured to a mount.

FIG. 5 is a side view showing the flue extension supported by the mount when the mount is in a first (operating) configuration.

FIG. 6 is a side view showing the flue extension supported by the mount when the mount is in a second (stowed) configuration.

FIG. 7 shows the flue extension supported by the mount in the first (operating) configuration, relative to an exhaust hood and cooking appliance.

FIG. 8 shows the flue extension supported by the mount in the second (stowed) configuration, relative to an exhaust hood and cooking appliance.

FIG. 9 is a perspective view of a heat exchanger assembly that is suitable for use in a system according to an embodiment.

FIG. 10 is a side view of the heat exchanger assembly of FIG. 9.

FIG. 11 is a perspective view of an alternative heat exchanger configuration.

DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable a person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the embodiments disclosed, but is to be accorded the widest scope consistent with the principles and features disclosed herein. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The phrase “heat exchanger assembly” is used interchangeably with the term “coil” throughout the description and in the claims.

FIG. 1 is a simplified block diagram showing the components of a system 100 according to an embodiment. A heat exchanger assembly 102 is disposed within a flue extension 104, which is supported by a not illustrated mount within a space 106 between a cooking appliance 108 and an exhaust hood 110. The heat exchanger assembly 102 is in fluid communication with a second heat exchanger assembly 112, which is disposed within a tank 114 containing a medium that is to be heated. For instance, tubing 116 and 118 are connected between the heat exchanger assembly 102 and the second heat exchanger assembly 112 for circulating a thermal fluid therebetween. For simplicity, various elements including sensors, controllers, manifolds, valves and pumps etc., which are described below with reference to FIG. 2, have been omitted from FIG. 1. The dashed lines in FIG. 1 represent data communication paths for receiving feedback signals and for providing control signals, and are intended to be illustrative in nature. In this example, both the medium that is to be heated and the thermal fluid are water. Optionally, the thermal fluid is another fluid, such as for instance a water/propylene glycol mixture, e.g. 60% propylene glycol and 40% water. Optionally, the configuration of the second heat exchanger assembly 112 differs from the configuration of the heat exchanger assembly 102.

FIG. 2 is a more detailed schematic diagram of system 100. Controller 120 receives feedback signals from temperature sensors 200 and from flow sensors 202. In the embodiment that is shown in FIG. 2, temperature sensors 200 are located: (1) in the tubing 118 before the inlet to the second heat exchanger assembly 112; (2) in the tubing 116 after the outlet from the second heat exchanger assembly 112; (3) in the cold water supply line before the inlet to the storage tank 114; and (4) in the hot water supply line after the outlet from the storage tank 114. A fifth temperature sensor 200 is disposed within the flue extension 104. The fifth temperature sensor is used to detect a temperature increase in the flue extension 104, which causes the system to switch on and begin sensing other parameters, etc. For instance, a relay is responsive to an output signal from the fifth temperature sensor for switching on and off a pump 206. Additionally, flow meters 202 are located in tubing 116 after the outlet from the second heat exchanger assembly 112 and in the cold water supply line before the inlet into the storage tank 114. Based on the signals that are received from the temperature sensors 200 and the flow meters 202, the controller 120 provides control signals for controlling various components of the system, such as for instance valves 204, pumps 206, etc. Optionally, the temperature sensors 200 and/or flow meters 202 and/or valves 204 and/or pumps 206 are disposed within the system 100 at other than the locations described above. Optionally, more or fewer temperature sensors 200 and/or flow meters 202 and/or valves 204 and/or pumps 206 are utilized in the system 100.

FIG. 3 is a simplified schematic diagram showing the components of a sensing and control sub-system of the system 100. Controller 120 includes a plurality of analog inputs (numbered 2, 3, 5-7, 9-12 in FIG. 3), which receive signals that are generated by various sensing devices in response to sensed system parameters. As discussed supra with reference to FIG. 2, in this specific and non-limiting example, the controller 120 receives signals from two flow meters 202 and from five temperature sensors 200. A display device 300, such as for instance an LCD screen, is provided for displaying at least some of the data that are read from the temperature sensors 200 and/or flow meters 202. Optionally, the display device 300 displays calculated values relating to the operation of the system 100, such as for instance the amount of money saved due to use of the system 100, the reduction in CO₂ emissions achieved, the amount of natural gas saved, etc.

Referring now to FIG. 4, shown is a perspective view of a mount 400 supporting flue extension 104. The mount 400 includes four wall-mounting brackets 404 (three are visible in FIG. 4), for securing the mount 400 to a support surface such as a wall (not shown in FIG. 4). For instance, the mount 400 is secured to the mounting surface using four ¼″ bolts (not shown in FIG. 4). The mount 400 includes left and right single link pivoting assemblies 406, which support generally vertical movement of the flue extension 104 between a first (operating) configuration in which the lower end of the flue extension 104 is aligned with but spaced apart from the flue of the cooking appliance (not shown in FIG. 4) by a first distance, and a second (stowed) configuration in which the lower end of the flue extension 104 is spaced apart from the flue of the cooking appliance by a second distance that is greater than the first distance. For instance, the flue extension 104 is supported in the first configuration during operation, in order to maximize heat transfer from the flue gas to the thermal fluid that is circulating within the heat exchanger assembly 102 (not shown in FIG. 4). On the other hand, the flue extension 104 is supported in the second configuration during cleaning and/or maintenance of the heat exchanger assembly 102 and/or cooking appliance and/or surrounding spaces. The single link pivoting assemblies 406 are pivotally attached to left and right frame-members 408, each of which is secured to a respective pair of the wall-mounting brackets 404. A handle 410 extends between the left and right single link pivoting assemblies 406, and may be grasped by a user when moving the flue extension 104 between the first and second configurations.

Of course, the material that is used to fabricate the flue extension 104 and the mount 400 must meet hygienic kitchen standards, must not corrode, and must be able to withstand the operating temperature of the cooking appliance 108. By way of a specific and non-limiting example, “403 stainless steel” is used.

FIG. 5 is a side view showing the flue extension 104 supported by the mount 400 in the first configuration, and FIG. 6 is a side view showing the flue extension 104 supported by the mount 400 in the second configuration. Additionally, FIGS. 7 and 8 show the flue extension 104 installed adjacent to a surface 700 via the mount 400. For improved clarity, the tubing 116 and 118 have been omitted from FIGS. 7 and 8. As is apparent, the mount 400 is supported entirely by the surface 700, which in this example is a wall that is situated behind the cooking appliance 108. None of the system components, including the mount 400, the flue extension 104, or the heat exchanger assembly 102, comes into contact with the cooking appliance 108 or with the exhaust hood 110. Accordingly, installing the system does not involve making any modifications to the cooking appliance 108 or to the exhaust hood 110.

Referring now to FIG. 9, shown is a perspective view of a heat exchanger assembly 102 that is suitable for use in the system 100 of FIG. 1. FIG. 10 shows a side view of the heat exchanger 102. In this specific and non-limiting example, the heat exchanger assembly 102 comprises tubing 900 that is fabricated from 13 mm (outside diameter) seamless 310s stainless steel, with a wall thickness of 1.0 mm, and with fins 902 that are made of 304 stainless steel. The tubing 900 is formed into an elongated, double helical coil configuration, having a height H, and a length L that is greater a width W. The values of H, L and W are limited by inter alia the physical size of the space 106 between the cooking appliance 108 and the exhaust hood 110. In a typical application, the length L of the coiled assembly is in the range 203-381 mm, and more preferably in the range 292-381 mm. Of course, these values are examples only and assume a length-wise restriction imposed by a commercial cooking appliance 108 having a flue width of 425 mm. In the specific and non-limiting example that is shown in FIGS. 9 and 10, the length L is approximately 304 mm, the width W is approximately 127 mm, and the height H is approximately 304 mm. The uncoiled length of the tubing 900 is approximately 6705 mm. Additionally, tube-end connectors 904 and 906 are provided at the opposite ends of the tube 900, for connecting the heat exchanger assembly 102 to the tubing 116 and 118. In practice, the tubing 116 and 118 may be standard flexible tubing, which may be routed or plumbed throughout the building and then transitioned to copper piping in the kitchen and finally to high temperature stainless steel flex lines for the final connection to inlets and outlets of the heat exchanger assembly 102.

In general, maximizing the outside diameter of the heat exchanger tube 900 and maximizing the number of turns of the coil, while also minimizing the wall thickness of the heat exchanger tubes 900, results in greater heat transfer to the thermal fluid and accordingly produces a higher thermal fluid outlet temperature. The spacing between adjacent turns of the coil is limited by the maximum allowable flue gas flow rate reduction. That is to say, packing the turns of the double helical coil too closely together causes a flow restriction, and the flue gas venting may become inadequate. In the heat exchanger assembly 102 that is shown in FIGS. 9 and 10, the center of the double helical coil is substantially open and thereby ensures adequate flow through the structure.

Alternatively, a heat exchanger assembly having a different shape and/or a different configuration may be used in the system 100. For instance a common “trombone-shaped” coil 1100, as shown in FIG. 11, may be used in place of the heat exchanger assembly 102 that is shown in FIGS. 9 and 10. Further alternatively, finless tubing or tubing that is fabricated from a different material etc. is used.

During operation the flue extension 104 is aligned above the flue 702 of the cooking appliance 108, as is shown in FIG. 7. An optional gasket 704 (shown using dashed lines), which is fabricated from a heat resistant material, is disposed between the flue extension 104 and the flue 702. Pump 206 (not shown in FIG. 7) circulates a thermal fluid through the tubing 900 of the not illustrated heat exchanger assembly 102. Flue gas is vented from the cooking appliance 108 via flue 702 and enters into the flue extension 104, optionally being guided by the gasket 704 when present. The flue gas flows around the finned tubing 900 of the heat exchanger assembly 102, which results in transfer of energy (heat) from the flue gas to the thermal fluid that is being circulated within the heat exchanger assembly 102. More particularly, the finned heat exchanger tubing 900 comprises a plurality of substantially straight tube sections that are arranged substantially normal to a flow direction of the flue gas through the flue extension. Pump 206 then causes the heated thermal fluid to flow out of the heat exchanger assembly 102 and into the second heat exchanger assembly 112, which is disposed within storage tank 114. Water stored within storage tank 114 absorbs energy (heat) from the thermal fluid, thereby raising the temperature of the stored water and lowering the temperature of the thermal fluid. The cooled thermal fluid exits the second heat exchanger assembly 112 and is then returned to the heat exchanger assembly 102, and the cycle repeats.

When maintenance or cleaning is required, a user simply grasps the handle 910 and pivots the flue extension 104 (including the optional gasket 704) upward and away from the flue 702 of cooking appliance 108. The flue 702 and/or surrounding surfaces etc., may then be cleaned, moved and/or maintained.

Providing a flue extension 104 in alignment with the flue 702 of the cooking appliance 108, and disposing the heat exchanger assembly 102 within the flue extension 104, avoids the need modify either the flue 702 or the exhaust hood 110. Further, the volume and pressure of the flue gas flow through the flue 702 and exhaust hood is substantially unaffected by the presence of the heat exchanger assembly 102 within the flue extension 104. Further still, the heat exchanger assembly 102 and flue extension 104 can be rapidly moved out of the way to provide access to the flue 702 when required, including in emergency situations. The flue extension 104 channels the flue gas upward and toward the exhaust hood, limiting the amount of heat that escapes into the environment around the cooking appliance. Additionally, the heat exchanger assembly 102 removes some of the heat from the flue gas, thereby lowering the temperature of the flue gas and further limiting the amount of heat that escapes into the environment around the cooking appliance.

Optionally, a different type of mount is used, such as for instance a “drawer-slider” type mount that support horizontal movement of the flue extension and heat exchanger assembly. Such a mount is appropriate when the vertical dimension of the space 106 between the cooking appliance 108 and exhaust hood 110 is limited. Alternatively, the mount is stationary and the flue extension 104 is secured to the mount using quick-release fasteners, or the flue extension 104 simply “snaps” into place on the mount, such that the flue extension 104 and heat exchanger assembly 102 may be removed from the mount for cleaning/maintenance purposes. Further alternatively, the flue extension 104 and heat exchanger assembly 102 may be suspended from the ceiling or from another support surface above the cooking appliance, such as for instance using cables or chains.

While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the invent of embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, and/or ordinary meanings of the defined terms. The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases.

Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

Numerical ranges include the end-point values that define the ranges. For instance, “between X and Y” includes both X and Y, as well as all temperature values between X and Y.

In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively.

The foregoing description of methods and embodiments of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention and all equivalents be defined by the claims appended hereto. 

What is claimed is:
 1. A system for extracting heat from a flue gas exiting from a cooking appliance, the system comprising: a flue extension having an open first end and an open second end opposite the first end, the first end aligned with but spaced apart from a flue of the cooking appliance for receiving a flue gas at a first temperature as it exits via the flue of the cooking appliance, and the second end facing but spaced apart from an exhaust hood for discharging the flue gas at a second temperature to the exhaust hood, the second temperature being lower than the first temperature; a mount for supporting the flue extension within a space between the flue of the cooking appliance and the exhaust hood, the mount being secured to a surface that is proximate the cooking appliance and that is other than a surface of either the cooking appliance or the exhaust hood; and a heat exchanger assembly disposed within the flue extension and comprising a heat exchanger tube for circulating a volume of a thermal fluid, the heat exchanger tube comprising a plurality of substantially straight tube sections that are arranged substantially normal to a flow direction of the flue gas through the flue extension.
 2. The system of claim 1, wherein the mount supports a movement of the flue extension between an operating configuration in which the first end of the flue extension is spaced apart from the flue of the cooking appliance by a first distance and a stowed configuration in which the first end of the flue extension is spaced apart from the flue of the cooking appliance by a second distance that is greater than the first distance.
 3. The system of claim 2, wherein the mount comprises a single link pivoting assembly.
 4. The system of claim 1, wherein the heat exchanger tube has an inlet end for receiving the volume of the thermal fluid into the heat exchanger tube and an outlet end for providing the volume of the thermal fluid out of the heat exchanger tube.
 5. The system of claim 4, further comprising a storage tank for containing a fluid medium that is to be heated and further comprising a second heat exchanger assembly disposed within the storage tank, an inlet end of the second heat exchanger assembly being in fluid communication with the outlet end of the heat exchanger tube and an outlet end of the second heat exchanger assembly being in fluid communication with the inlet end of the heat exchanger tube.
 6. The system of claim 5, further comprising a pump for circulating the thermal fluid within a closed circuit that includes the heat exchanger assembly and the second heat exchanger assembly.
 7. The system of claim 1, wherein the heat exchanger tube comprises a plurality of external fins for increasing a total area of thermal contact with the flue gas.
 8. A system for extracting heat from a flue gas exiting from a cooking appliance, comprising: a flue extension having an open first end, an open second end that is opposite the first end, and a central passageway extending between the first and second ends; a first heat exchanger assembly disposed within the central passageway of the flue extension; a mount for supporting the flue extension and the first heat exchanger within a space between a flue of the cooking appliance and an exhaust hood disposed above the cooking appliance, the mount being operable between: i) a first configuration in which the first end of the flue extension is aligned with but spaced apart from the flue of the cooking appliance by a first distance, and ii) a second configuration in which the first end of the flue extension is spaced apart from the flue of the cooking appliance by a second distance that is greater than the first distance; a storage tank for containing a medium to be heated; a second heat exchanger disposed within the storage tank, the second heat exchanger being in fluid communication with the first heat exchanger; and a pump for circulating a thermal fluid within a closed circuit that includes the first heat exchanger and the second heat exchanger.
 9. The system of claim 8, further comprising at least one temperature sensor and at least one flow meter for measuring a temperature and a flow rate, respectively, of the thermal fluid.
 10. The system of claim 9, further comprising a controller that is responsive to data signals provided from the at least one temperature sensor and from the at least one flow meter for controlling the circulating of the thermal fluid within the closed circuit.
 11. The system of claim 8, wherein the first heat exchanger assembly comprises a heat exchanger tube for circulating a volume of the thermal fluid, the heat exchanger tube comprising a plurality of substantially straight tube sections that are arranged substantially normal to a flow direction of the flue gas through the flue extension.
 12. The system of claim 11, wherein the heat exchanger tube has an inlet end for receiving the volume of the thermal fluid into the heat exchanger tube and an outlet end for providing the volume of the thermal fluid out of the heat exchanger tube.
 13. The system of claim 11, wherein the heat exchanger tube comprises a plurality of external fins for increasing a total area of thermal contact with the flue gas.
 14. The system of claim 8, wherein the mount comprises a single link pivoting assembly.
 15. The system of claim 8, further comprising a gasket that extends between the first end of the flue extension and the flue of the cooking appliance when the mount is in the first configuration, the gasket for guiding a flow of the flue gas into the central passageway of the flue extension.
 16. A method for extracting heat from a flue gas exiting a cooking appliance, comprising: using a mount, supporting a flue extension between a flue of the cooking apparatus and an exhaust hood disposed above the cooking apparatus, such that an open first end of the flue extension is aligned with but spaced apart from the flue of the cooking apparatus by a first distance, and wherein the mount is secured to a surface that is proximate the cooking appliance and that is other than a surface of either the cooking appliance or the exhaust hood; providing a heat exchanger assembly within the flue extension, the heat exchanger assembly including a heat exchanger coil; receiving the flue gas via the open first end of the flue extension, the flue gas being constrained by the flue extension to flow around the heat exchanger coil and out through an open second end of the flue extension along a direction generally toward the exhaust hood; and while the flue gas is being constrained to flow around the heat exchanger coil, circulating a thermal fluid within the heat exchanger coil, whereby heat is transferred from the flue gas to the thermal fluid.
 17. The method of claim 16, further comprising circulating the thermal fluid from the heat exchanger assembly to a second heat exchanger assembly disposed within a storage tank containing a medium that is to be heated.
 18. The method of claim 16, further comprising actuating the mount into a stowed configuration in which the first end of the flue extension is spaced apart from the flue of the cooking appliance by a second distance that is greater than the first distance.
 19. The method of claim 16, wherein the thermal fluid is water.
 20. The method of claim 16, comprising sensing a temperature and a flow rate of the thermal fluid, and in response to the sensed temperature and sensed flow rate controlling the circulating of the thermal fluid. 